Apparatus for measuring blowby of gasses past the pistons of an internal combustion engine are known in the art. These heretofore utilized apparatus generally had features which decreased the accuracy of the resultant measurement. Entrained water in the form of droplets was one of the major problems. Previous devices either removed the water from the flow stream, thus reducing accuracy; or kept the water in the flow stream with subsequent short term measurement functionally due to fouling of the flow meter by the mixture of water and other blowby constituents. Some used heavy filtering to clean the flow stream which resulted in a back pressure on the engine which was detrimental to normal engine operation. The present invention is directed to overcoming one or more of the problems of presently available apparatus.